swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0

swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0

[Mikhail Gavrilov]

Hi folks,
today I joined to testing Kernel 5.10 and see that every boot happens
this warning:

[    9.032096] ======================================================
[    9.032097] WARNING: possible circular locking dependency detected
[    9.032098] 5.10.0-0.rc0.20201014gitb5fc7a89e58b.41.fc34.x86_64 #1
Not tainted
[    9.032099] ------------------------------------------------------
[    9.032100] swapon/913 is trying to acquire lock:
[    9.032101] ffffc984fda4f948 (&zstrm->lock){+.+.}-{2:2}, at:
zcomp_stream_get+0x5/0x90 [zram]
[    9.032106]
               but task is already holding lock:
[    9.032107] ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at:
zs_map_object+0x7a/0x2e0
[    9.032111]
               which lock already depends on the new lock.

[    9.032112]
               the existing dependency chain (in reverse order) is:
[    9.032112]
               -> #1 (&zspage->lock){.+.+}-{2:2}:
[    9.032116]        _raw_read_lock+0x3d/0xa0
[    9.032118]        zs_map_object+0x7a/0x2e0
[    9.032119]        zram_bvec_rw.constprop.0.isra.0+0x287/0x730 [zram]
[    9.032121]        zram_submit_bio+0x189/0x35d [zram]
[    9.032123]        submit_bio_noacct+0xff/0x650
[    9.032124]        submit_bh_wbc+0x17d/0x1a0
[    9.032126]        __block_write_full_page+0x227/0x580
[    9.032128]        __writepage+0x1a/0x70
[    9.032129]        write_cache_pages+0x21c/0x540
[    9.032130]        generic_writepages+0x41/0x60
[    9.032131]        do_writepages+0x28/0xb0
[    9.032133]        __filemap_fdatawrite_range+0xa7/0xe0
[    9.032134]        file_write_and_wait_range+0x67/0xb0
[    9.032135]        blkdev_fsync+0x17/0x40
[    9.032137]        __x64_sys_fsync+0x34/0x60
[    9.032138]        do_syscall_64+0x33/0x40
[    9.032140]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[    9.032140]
               -> #0 (&zstrm->lock){+.+.}-{2:2}:
[    9.032144]        __lock_acquire+0x11e3/0x21f0
[    9.032145]        lock_acquire+0xc8/0x400
[    9.032146]        zcomp_stream_get+0x38/0x90 [zram]
[    9.032148]        zram_bvec_rw.constprop.0.isra.0+0x4c1/0x730 [zram]
[    9.032149]        zram_rw_page+0xa9/0x130 [zram]
[    9.032150]        bdev_read_page+0x71/0xa0
[    9.032151]        do_mpage_readpage+0x5a8/0x800
[    9.032152]        mpage_readahead+0xfb/0x230
[    9.032153]        read_pages+0x60/0x1e0
[    9.032154]        page_cache_readahead_unbounded+0x1da/0x270
[    9.032155]        generic_file_buffered_read+0x69c/0xe00
[    9.032156]        new_sync_read+0x108/0x180
[    9.032157]        vfs_read+0x12e/0x1c0
[    9.032158]        ksys_read+0x58/0xd0
[    9.032159]        do_syscall_64+0x33/0x40
[    9.032160]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[    9.032161]
               other info that might help us debug this:

[    9.032162]  Possible unsafe locking scenario:

[    9.032162]        CPU0                    CPU1
[    9.032163]        ----                    ----
[    9.032163]   lock(&zspage->lock);
[    9.032165]                                lock(&zstrm->lock);
[    9.032166]                                lock(&zspage->lock);
[    9.032167]   lock(&zstrm->lock);
[    9.032168]
                *** DEADLOCK ***

[    9.032169] 1 lock held by swapon/913:
[    9.032170]  #0: ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at:
zs_map_object+0x7a/0x2e0
[    9.032172]
               stack backtrace:
[    9.032174] CPU: 14 PID: 913 Comm: swapon Not tainted
5.10.0-0.rc0.20201014gitb5fc7a89e58b.41.fc34.x86_64 #1
[    9.032175] Hardware name: System manufacturer System Product
Name/ROG STRIX X570-I GAMING, BIOS 2606 08/13/2020
[    9.032176] Call Trace:
[    9.032179]  dump_stack+0x8b/0xb0
[    9.032181]  check_noncircular+0xd0/0xf0
[    9.032183]  __lock_acquire+0x11e3/0x21f0
[    9.032185]  lock_acquire+0xc8/0x400
[    9.032187]  ? zcomp_stream_get+0x5/0x90 [zram]
[    9.032189]  zcomp_stream_get+0x38/0x90 [zram]
[    9.032190]  ? zcomp_stream_get+0x5/0x90 [zram]
[    9.032192]  zram_bvec_rw.constprop.0.isra.0+0x4c1/0x730 [zram]
[    9.032194]  ? __part_start_io_acct+0x4d/0xf0
[    9.032196]  zram_rw_page+0xa9/0x130 [zram]
[    9.032197]  bdev_read_page+0x71/0xa0
[    9.032199]  do_mpage_readpage+0x5a8/0x800
[    9.032201]  ? xa_load+0xbf/0x140
[    9.032203]  mpage_readahead+0xfb/0x230
[    9.032205]  ? bdev_evict_inode+0x1a0/0x1a0
[    9.032207]  read_pages+0x60/0x1e0
[    9.032208]  page_cache_readahead_unbounded+0x1da/0x270
[    9.032211]  generic_file_buffered_read+0x69c/0xe00
[    9.032213]  new_sync_read+0x108/0x180
[    9.032215]  vfs_read+0x12e/0x1c0
[    9.032217]  ksys_read+0x58/0xd0
[    9.032218]  do_syscall_64+0x33/0x40
[    9.032219]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[    9.032221] RIP: 0033:0x7ff6fcb8e432
[    9.032222] Code: c0 e9 b2 fe ff ff 50 48 8d 3d e2 39 0a 00 e8 a5
f0 01 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75
10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89
54 24
[    9.032223] RSP: 002b:00007ffff64ee858 EFLAGS: 00000246 ORIG_RAX:
0000000000000000
[    9.032225] RAX: ffffffffffffffda RBX: 00007ffff64eea10 RCX: 00007ff6fcb8e432
[    9.032226] RDX: 0000000000010000 RSI: 000055a78c4990c0 RDI: 0000000000000003
[    9.032227] RBP: 0000000000000003 R08: 000055a78c4990c0 R09: 00007ff6fcc60a60
[    9.032228] R10: 0000000000000430 R11: 0000000000000246 R12: 00007ffff64eeaf0
[    9.032228] R13: 000055a78c4990c0 R14: 0000000000000000 R15: 00007ffff64eeaf0

reproductivity 100% reliable on my system

$ /usr/src/kernels/`uname -r`/scripts/faddr2line
/lib/debug/lib/modules/`uname
-r`/kernel/drivers/block/zram/zram.ko.debug zcomp_stream_get+0x5
zcomp_stream_get+0x5/0x10:
zcomp_stream_get at
/usr/src/debug/kernel-20201014gitb5fc7a89e58b/linux-5.10.0-0.rc0.20201014gitb5fc7a89e58b.41.fc34.x86_64/drivers/block/zram/zcomp.c:111

$ git blame -L 106,116 drivers/block/zram/zcomp.c
Blaming lines:   4% (11/232), done.
56b4e8cb85827 (Sergey Senozhatsky 2014-04-07 15:38:22 -0700 106)
 sz += scnprintf(buf + sz, PAGE_SIZE - sz, "\n");
e46b8a030d76d (Sergey Senozhatsky 2014-04-07 15:38:17 -0700 107)
 return sz;
e46b8a030d76d (Sergey Senozhatsky 2014-04-07 15:38:17 -0700 108) }
e46b8a030d76d (Sergey Senozhatsky 2014-04-07 15:38:17 -0700 109)
2aea8493d326b (Sergey Senozhatsky 2016-07-26 15:22:42 -0700 110)
struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
e7e1ef439d18f (Sergey Senozhatsky 2014-04-07 15:38:11 -0700 111) {
19f545b6e07f7 (Mike Galbraith     2020-05-27 22:11:19 +0200 112)
 local_lock(&comp->stream->lock);
19f545b6e07f7 (Mike Galbraith     2020-05-27 22:11:19 +0200 113)
 return this_cpu_ptr(comp->stream);
e7e1ef439d18f (Sergey Senozhatsky 2014-04-07 15:38:11 -0700 114) }
e7e1ef439d18f (Sergey Senozhatsky 2014-04-07 15:38:11 -0700 115)
2aea8493d326b (Sergey Senozhatsky 2016-07-26 15:22:42 -0700 116) void
zcomp_stream_put(struct zcomp *comp)


$ /usr/src/kernels/`uname -r`/scripts/faddr2line
/lib/debug/lib/modules/`uname -r`/vmlinux zs_map_object+0x7a
zs_map_object+0x7a/0x2e0:
get_zspage_mapping at mm/zsmalloc.c:518
(inlined by) zs_map_object at mm/zsmalloc.c:1325


$ git blame -L 1320,1330 mm/zsmalloc.c
Blaming lines:   0% (11/2594), done.
3783689a1aa82 (Minchan Kim      2016-07-26 15:23:23 -0700 1320)
 zspage = get_zspage(page);
48b4800a1c6af (Minchan Kim      2016-07-26 15:23:31 -0700 1321)
48b4800a1c6af (Minchan Kim      2016-07-26 15:23:31 -0700 1322)
 /* migration cannot move any subpage in this zspage */
48b4800a1c6af (Minchan Kim      2016-07-26 15:23:31 -0700 1323)
 migrate_read_lock(zspage);
48b4800a1c6af (Minchan Kim      2016-07-26 15:23:31 -0700 1324)
3783689a1aa82 (Minchan Kim      2016-07-26 15:23:23 -0700 1325)
 get_zspage_mapping(zspage, &class_idx, &fg);
66cdef663cd7a (Ganesh Mahendran 2014-12-18 16:17:40 -0800 1326)
 class = pool->size_class[class_idx];
bfd093f5e7f09 (Minchan Kim      2016-07-26 15:23:28 -0700 1327)
 off = (class->size * obj_idx) & ~PAGE_MASK;
df8b5bb998f10 (Ganesh Mahendran 2014-12-12 16:57:07 -0800 1328)
66cdef663cd7a (Ganesh Mahendran 2014-12-18 16:17:40 -0800 1329)
 area = &get_cpu_var(zs_map_area);
66cdef663cd7a (Ganesh Mahendran 2014-12-18 16:17:40 -0800 1330)
 area->vm_mm = mm;


The last changes were made by Mike and acked by Peter. That is why I
invited you here, can you clarify the situation.

--
Best Regards,
Mike Gavrilov.

Re: swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0

[Peter Zijlstra]

On Fri, Oct 16, 2020 at 11:21:47AM +0500, Mikhail Gavrilov wrote:
> Hi folks,
> today I joined to testing Kernel 5.10 and see that every boot happens
> this warning:
> 
> [    9.032096] ======================================================
> [    9.032097] WARNING: possible circular locking dependency detected
> [    9.032098] 5.10.0-0.rc0.20201014gitb5fc7a89e58b.41.fc34.x86_64 #1 Not tainted
> [    9.032099] ------------------------------------------------------
> [    9.032100] swapon/913 is trying to acquire lock:
> [    9.032101] ffffc984fda4f948 (&zstrm->lock){+.+.}-{2:2}, at: zcomp_stream_get+0x5/0x90 [zram]
> [    9.032106] but task is already holding lock:
> [    9.032107] ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at: zs_map_object+0x7a/0x2e0
> [    9.032111] which lock already depends on the new lock.
> [    9.032112] the existing dependency chain (in reverse order) is:

> [    9.032112] -> #1 (&zspage->lock){.+.+}-{2:2}:
> [    9.032116]        _raw_read_lock+0x3d/0xa0
> [    9.032118]        zs_map_object+0x7a/0x2e0
> [    9.032119]        zram_bvec_rw.constprop.0.isra.0+0x287/0x730 [zram]
> [    9.032121]        zram_submit_bio+0x189/0x35d [zram]
> [    9.032123]        submit_bio_noacct+0xff/0x650
> [    9.032124]        submit_bh_wbc+0x17d/0x1a0
> [    9.032126]        __block_write_full_page+0x227/0x580
> [    9.032128]        __writepage+0x1a/0x70
> [    9.032129]        write_cache_pages+0x21c/0x540
> [    9.032130]        generic_writepages+0x41/0x60
> [    9.032131]        do_writepages+0x28/0xb0
> [    9.032133]        __filemap_fdatawrite_range+0xa7/0xe0
> [    9.032134]        file_write_and_wait_range+0x67/0xb0
> [    9.032135]        blkdev_fsync+0x17/0x40
> [    9.032137]        __x64_sys_fsync+0x34/0x60
> [    9.032138]        do_syscall_64+0x33/0x40
> [    9.032140]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [    9.032140]
>                -> #0 (&zstrm->lock){+.+.}-{2:2}:


> [    9.032169] 1 lock held by swapon/913:
> [    9.032170]  #0: ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at: zs_map_object+0x7a/0x2e0

> [    9.032176] Call Trace:
> [    9.032179]  dump_stack+0x8b/0xb0
> [    9.032181]  check_noncircular+0xd0/0xf0
> [    9.032183]  __lock_acquire+0x11e3/0x21f0
> [    9.032185]  lock_acquire+0xc8/0x400
> [    9.032187]  ? zcomp_stream_get+0x5/0x90 [zram]
> [    9.032189]  zcomp_stream_get+0x38/0x90 [zram]
> [    9.032190]  ? zcomp_stream_get+0x5/0x90 [zram]
> [    9.032192]  zram_bvec_rw.constprop.0.isra.0+0x4c1/0x730 [zram]
> [    9.032194]  ? __part_start_io_acct+0x4d/0xf0
> [    9.032196]  zram_rw_page+0xa9/0x130 [zram]
> [    9.032197]  bdev_read_page+0x71/0xa0
> [    9.032199]  do_mpage_readpage+0x5a8/0x800
> [    9.032201]  ? xa_load+0xbf/0x140
> [    9.032203]  mpage_readahead+0xfb/0x230
> [    9.032205]  ? bdev_evict_inode+0x1a0/0x1a0
> [    9.032207]  read_pages+0x60/0x1e0
> [    9.032208]  page_cache_readahead_unbounded+0x1da/0x270
> [    9.032211]  generic_file_buffered_read+0x69c/0xe00
> [    9.032213]  new_sync_read+0x108/0x180
> [    9.032215]  vfs_read+0x12e/0x1c0
> [    9.032217]  ksys_read+0x58/0xd0
> [    9.032218]  do_syscall_64+0x33/0x40
> [    9.032219]  entry_SYSCALL_64_after_hwframe+0x44/0xa9


Joy... __zram_bvec_write() and __zram_bvec_read() take these locks in
opposite order.

Does something like the (_completely_) untested below cure things?

---

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9100ac36670a..c1e2c2e1cde8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1216,10 +1216,11 @@ static void zram_free_page(struct zram *zram, size_t index)
 static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 				struct bio *bio, bool partial_io)
 {
-	int ret;
+	struct zcomp_strm *zstrm;
 	unsigned long handle;
 	unsigned int size;
 	void *src, *dst;
+	int ret;
 
 	zram_slot_lock(zram, index);
 	if (zram_test_flag(zram, index, ZRAM_WB)) {
@@ -1250,6 +1251,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 
 	size = zram_get_obj_size(zram, index);
 
+	if (size != PAGE_SIZE)
+		zstrm = zcomp_stream_get(zram->comp);
+
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
 		dst = kmap_atomic(page);
@@ -1257,8 +1261,6 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		kunmap_atomic(dst);
 		ret = 0;
 	} else {
-		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
-
 		dst = kmap_atomic(page);
 		ret = zcomp_decompress(zstrm, src, size, dst);
 		kunmap_atomic(dst);

Re: swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0

[Mikhail Gavrilov]

On Fri, 16 Oct 2020 at 17:40, Peter Zijlstra <peterz@infradead.org> wrote:
>
>
> Joy... __zram_bvec_write() and __zram_bvec_read() take these locks in
> opposite order.
>
> Does something like the (_completely_) untested below cure things?

Excellent! This patch (_completely_) cured all other warnings which
were present in the log.
dmesg before patch: https://pastebin.com/tZY3npHG
dmesg after patch: https://pastebin.com/iD7ZL1mb

Thanks!

--
Best Regards,
Mike Gavrilov.

Re: swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0

[Minchan Kim]

On Fri, Oct 16, 2020 at 02:40:09PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 16, 2020 at 11:21:47AM +0500, Mikhail Gavrilov wrote:
> > Hi folks,
> > today I joined to testing Kernel 5.10 and see that every boot happens
> > this warning:
> > 
> > [    9.032096] ======================================================
> > [    9.032097] WARNING: possible circular locking dependency detected
> > [    9.032098] 5.10.0-0.rc0.20201014gitb5fc7a89e58b.41.fc34.x86_64 #1 Not tainted
> > [    9.032099] ------------------------------------------------------
> > [    9.032100] swapon/913 is trying to acquire lock:
> > [    9.032101] ffffc984fda4f948 (&zstrm->lock){+.+.}-{2:2}, at: zcomp_stream_get+0x5/0x90 [zram]
> > [    9.032106] but task is already holding lock:
> > [    9.032107] ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at: zs_map_object+0x7a/0x2e0
> > [    9.032111] which lock already depends on the new lock.
> > [    9.032112] the existing dependency chain (in reverse order) is:
> 
> > [    9.032112] -> #1 (&zspage->lock){.+.+}-{2:2}:
> > [    9.032116]        _raw_read_lock+0x3d/0xa0
> > [    9.032118]        zs_map_object+0x7a/0x2e0
> > [    9.032119]        zram_bvec_rw.constprop.0.isra.0+0x287/0x730 [zram]
> > [    9.032121]        zram_submit_bio+0x189/0x35d [zram]
> > [    9.032123]        submit_bio_noacct+0xff/0x650
> > [    9.032124]        submit_bh_wbc+0x17d/0x1a0
> > [    9.032126]        __block_write_full_page+0x227/0x580
> > [    9.032128]        __writepage+0x1a/0x70
> > [    9.032129]        write_cache_pages+0x21c/0x540
> > [    9.032130]        generic_writepages+0x41/0x60
> > [    9.032131]        do_writepages+0x28/0xb0
> > [    9.032133]        __filemap_fdatawrite_range+0xa7/0xe0
> > [    9.032134]        file_write_and_wait_range+0x67/0xb0
> > [    9.032135]        blkdev_fsync+0x17/0x40
> > [    9.032137]        __x64_sys_fsync+0x34/0x60
> > [    9.032138]        do_syscall_64+0x33/0x40
> > [    9.032140]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [    9.032140]
> >                -> #0 (&zstrm->lock){+.+.}-{2:2}:
> 
> 
> > [    9.032169] 1 lock held by swapon/913:
> > [    9.032170]  #0: ffff993c54cdceb0 (&zspage->lock){.+.+}-{2:2}, at: zs_map_object+0x7a/0x2e0
> 
> > [    9.032176] Call Trace:
> > [    9.032179]  dump_stack+0x8b/0xb0
> > [    9.032181]  check_noncircular+0xd0/0xf0
> > [    9.032183]  __lock_acquire+0x11e3/0x21f0
> > [    9.032185]  lock_acquire+0xc8/0x400
> > [    9.032187]  ? zcomp_stream_get+0x5/0x90 [zram]
> > [    9.032189]  zcomp_stream_get+0x38/0x90 [zram]
> > [    9.032190]  ? zcomp_stream_get+0x5/0x90 [zram]
> > [    9.032192]  zram_bvec_rw.constprop.0.isra.0+0x4c1/0x730 [zram]
> > [    9.032194]  ? __part_start_io_acct+0x4d/0xf0
> > [    9.032196]  zram_rw_page+0xa9/0x130 [zram]
> > [    9.032197]  bdev_read_page+0x71/0xa0
> > [    9.032199]  do_mpage_readpage+0x5a8/0x800
> > [    9.032201]  ? xa_load+0xbf/0x140
> > [    9.032203]  mpage_readahead+0xfb/0x230
> > [    9.032205]  ? bdev_evict_inode+0x1a0/0x1a0
> > [    9.032207]  read_pages+0x60/0x1e0
> > [    9.032208]  page_cache_readahead_unbounded+0x1da/0x270
> > [    9.032211]  generic_file_buffered_read+0x69c/0xe00
> > [    9.032213]  new_sync_read+0x108/0x180
> > [    9.032215]  vfs_read+0x12e/0x1c0
> > [    9.032217]  ksys_read+0x58/0xd0
> > [    9.032218]  do_syscall_64+0x33/0x40
> > [    9.032219]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> 
> Joy... __zram_bvec_write() and __zram_bvec_read() take these locks in
> opposite order.
> 
> Does something like the (_completely_) untested below cure things?


[19f545b6e07f7, zram: Use local lock to protect per-CPU data] introduced
new lock dependency and this patch looks good to me.

Peter, do you mind sending this patch with fix tag to Andrew Morton?

Thanks for your help.

> 
> ---
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 9100ac36670a..c1e2c2e1cde8 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1216,10 +1216,11 @@ static void zram_free_page(struct zram *zram, size_t index)
>  static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
>  				struct bio *bio, bool partial_io)
>  {
> -	int ret;
> +	struct zcomp_strm *zstrm;
>  	unsigned long handle;
>  	unsigned int size;
>  	void *src, *dst;
> +	int ret;
>  
>  	zram_slot_lock(zram, index);
>  	if (zram_test_flag(zram, index, ZRAM_WB)) {
> @@ -1250,6 +1251,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
>  
>  	size = zram_get_obj_size(zram, index);
>  
> +	if (size != PAGE_SIZE)
> +		zstrm = zcomp_stream_get(zram->comp);
> +
>  	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
>  	if (size == PAGE_SIZE) {
>  		dst = kmap_atomic(page);
> @@ -1257,8 +1261,6 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
>  		kunmap_atomic(dst);
>  		ret = 0;
>  	} else {
> -		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
> -
>  		dst = kmap_atomic(page);
>  		ret = zcomp_decompress(zstrm, src, size, dst);
>  		kunmap_atomic(dst);

[PATCH] zram: Fix __zram_bvec_{read,write}() locking order

[Peter Zijlstra]

Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
__zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.

Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
 drivers/block/zram/zram_drv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9100ac36670a..c1e2c2e1cde8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1216,10 +1216,11 @@ static void zram_free_page(struct zram *zram, size_t index)
 static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 				struct bio *bio, bool partial_io)
 {
-	int ret;
+	struct zcomp_strm *zstrm;
 	unsigned long handle;
 	unsigned int size;
 	void *src, *dst;
+	int ret;
 
 	zram_slot_lock(zram, index);
 	if (zram_test_flag(zram, index, ZRAM_WB)) {
@@ -1250,6 +1251,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 
 	size = zram_get_obj_size(zram, index);
 
+	if (size != PAGE_SIZE)
+		zstrm = zcomp_stream_get(zram->comp);
+
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
 		dst = kmap_atomic(page);
@@ -1257,8 +1261,6 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		kunmap_atomic(dst);
 		ret = 0;
 	} else {
-		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
-
 		dst = kmap_atomic(page);
 		ret = zcomp_decompress(zstrm, src, size, dst);
 		kunmap_atomic(dst);

Re: [PATCH] zram: Fix __zram_bvec_{read,write}() locking order

[Minchan Kim]

On Mon, Oct 19, 2020 at 12:13:53PM +0200, Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.
> 
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>

Thanks for the fix.

Re: [PATCH] zram: Fix __zram_bvec_{read,write}() locking order

[Sebastian Andrzej Siewior]

On 2020-10-19 12:13:53 [+0200], Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.
> 
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>

We have the same patch in RT. I didn't submit it with the other
local-lock patches because this splat pops up once pin_tag() is made a
sleeping lock. I missed the part where migrate_read_lock() can be a
lock. So:

Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian

Re: [PATCH] zram: Fix __zram_bvec_{read,write}() locking order

[Jens Axboe]

On 10/19/20 4:13 AM, Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.

Applied, thanks.

-- 
Jens Axboe